Measurements of liquid quantities and their flow velocities are covered in a large field of fluid and process engineering by through-flow or volumetric measurement systems that operate according to the positive displacement principle.
In these measurement systems, the requirements particularly for measurement precision and dynamic range are very high in the respective processes.
These processes particularly involve those processes in which a control, monitoring or testing must be conducted with maximum speed and precision.
In addition, a plurality of processes (e.g., liquids having different physical properties) are conducted, often with the same unit, which in turn places high requirements for the bandwidth of the operational capability of the entire system.
The invention shall meet the above-named requirements to the greatest extent. For this, first the functional interplay between the mechanical and the electronic components fitting most precisely in the through-flow or volumetric measurement system must be selected. After this, the design of the electronic unit is most important: it must be designed correspondingly as technically more efficient, more powerful, and more flexible. The entire measurement system as well as the method belonging to it and the corresponding arrangement shall be more intelligent, more robust and more user-friendly than the solutions known previously in the prior art.
As the basis for a higher efficiency, a higher resolution is necessary, which can be already produced by WO 2005/119 185 A1. In this case, a flow rate sensor has a measurement chamber, into which a medium whose volume and/or flow velocity will be measured can be introduced and can again be discharged. Freely rotatable mounted operating elements for measurement are found in the measurement chamber. Over and above this, at least one sensor is provided for the measurement of magnetic fields and/or changes of magnetic fields, and also a circuit means is provided, into which the output signals of the one or more sensors will be introduced. The one or more sensors provide an output signal and introduce it to the circuit means. The initial signal fluctuates periodically between a minimum value and a maximum value for each passage of an individual tooth and tooth gap belonging thereto of one of the measurement operating elements. Depending on the position of the tooth relative to the one or more sensors, the output signal assumes a reproducible intermediate value. The circuit means is constructed in such a way that it forms its own output signals from the output signals of the one or more sensors, and the circuit output signals convert the intermediate values into countable values that are representative of the partial volumes for the volumes transported between two teeth.
Positive displacement counters are rigidly clamped in the liquid column and any movement in the fluid circuit is recognized in this way. This is a very great advantage for the dynamics of the measurement system.
System oscillations may occur, however. Such oscillations may occur both in flow rest phases or also in the operating flow during flow phases. These oscillations are also recorded, adversely affecting the precision of the entire system. Consequently, during the measurement, pulses are also generated from the measurement system that are erroneously interpreted by electronic evaluations. This “negative” sensitivity in this case is increased still further by an increase in resolution or an interpolation factor. In each case depending on the intensity of the oscillations, error signals can be generated in the form of single-channel pulses or pulse sequences in the direction of through flow (preferred direction) or in the direction opposite to this operating direction.
Problematic in the measurement and evaluation systems and methods known previously in the prior art is the difficulty of exact measurement, taking into consideration possible system oscillations as well as disruptive and difficult process conditions, or the like.
Disruptive and difficult process conditions include, for example, the previously discussed fluctuations in the liquid column in the fluid system during flow rest phases, discontinuous flows with fluctuations in the direction opposite to the flow direction, a large flow bandwidth having high resolution requirements along with processing limits of the evaluation units, as well as increased demands for precision.
In further detail, the following undesired phenomena to be avoided as well as their causes are, in particular:
When clocked system components are present in the fluid circuit, such as, e.g., servo valves with dithers, or vibrations are present in system parts, such as, for example, a piston pump in free cycle, fluctuations of the liquid column arise in the fluid system during flow rest phases.
Discontinuous flows with fluctuations in the direction opposite to the flow direction arise, e.g., in process engineering in the case of a multi-component system, in which highly viscous adhesives or sealants are transported. Transport is conducted, e.g., by piston pumps that can also generate flows opposite to the preferred direction, due to their stroke movements, e.g., during the intake phase.
The physical properties of liquids are always dependent on ambient properties. Liquids practically adapt to their surroundings, whereby different physical phenomena result that are consequently of great importance correspondingly in the flow measurement.
Belonging to the variable physical properties under specific influences or process conditions are, in particular, the flow property, the fluidity (also called “inner friction”), the ratio of mass to volume of the liquid, the almost free displacement capability of the liquid molecules, friction between the liquid surfaces and the mechanical surfaces (also called “outer friction”), friction between the mechanical surfaces such as, e.g., bearings, changes in dimensions of the metal system components.
The process conditions are specified by the following factors:
Pressure in the fluid system, temperature of the fluid and of the environment, flow velocities, construction and material of the mechanical system components;
All of these physical factors in some way affect the precision in flow measurement technology, including positive displacement counters.
Said set of problems results from the requirement for increased precision. In many processes, the most highly precise measurements are demanded. The precision in the case of positive displacement counters will be influenced, in particular, by the liquid properties under the process-conditioned environment and the actual flow. The displaced volume changes slightly with the physical properties of the liquid under the respective conditions, such as pressure, temperature, and flow velocity, whereby deviations arise in the measurements.
For the most precise measurement requirements, the user must correspondingly adjust the pulse value of the output signals for the respective flow and the physical properties of the liquid in his evaluation. These parameters for the respective regions and corresponding to the physical properties of the liquid or the real displaced volume under the process conditions are normally taken up or filed in a reference table, a look-up table (abbrev.: LUT), this table being programmed in a downstream evaluation unit. With the values from the look-up table and a conversion algorithm, the evaluation of the corresponding pulse value is then conducted. This method, however, means a higher expenditure for the user, since for the most part the user needs to conduct a long startup procedure due to programming the parameters on his evaluation unit and in particular, needs to post-process the measurement results in a very time-consuming manner, which leads to a valuable loss of time and considerably more cost.
In particular, the measurement will have already been set in the measuring instrument, taking into consideration the above-named secondary physical conditions, and not set for the first time subsequently in a post-processing step.
Another problem is the desired high bandwidth of volumetric flows to be measured, i.e., a large flow bandwidth with high requirements for resolution along with processing limits of the evaluation units.
In several units, it may happen that the flow or volume measurement system needs to be operated over its entire volume or flow measurement range. Or, it may even be the case that different flow quantities or velocities must be run in one process or in several processes.
Additionally, however, the user would like to obtain as much information as possible of which of the interpolation methods described here can be produced due to the higher resolution. It can be a problem, however, to precisely set the correct interpolation factor. With high flow quantities or velocities, it may happen that the initial frequency for the downstream evaluation unit can no longer be processed. On the other hand, the resolution is for the most part too low for the user in the case of a smaller interpolation factor and small flow quantities or low velocities. For the most part, several system components, e.g. in the form of two switchable fluid circuits with displacement counters of different structural size, are used for solving this set of problems. Therefore, a possibility will be created so as to cover a broad bandwidth of different flow volumes with one measurement system.
The object of the present invention is to indicate a method for measuring a volumetric flow of a fluid in a preferred direction by means of a volume measurement device, which considers the above-named problems and permits, in particular, a user-friendly, time-saving and precise, as well as exact measurement.
Further, it is an object of the invention to indicate a method for measuring a volumetric flow by means of a quadrature signal, comprising a first signal of a first sensor and a second signal of a second sensor having identical angular frequency co, which are phase-shifted by 90° relative to one another, wherein the quadrature signal serves to determine the through-flow of a fluid in a preferred direction by means of a volume measurement device having an electronic circuit, by means of which the bandwidth of the measurement is increased, whereby measurement precision is further increased.
Another object of the invention is to indicate a volume measurement device for conducting a measurement method and a programmable process computer unit having at least one quadrature encoder interface/quadrature encoder counter for use in a volume measurement device for measuring a volumetric flow, which make possible a problem-free measurement of a volumetric flow.